Computer systems often generate data that needs to be stored persistently. System settings, digital photographs, electronic documents, and digital videos are all examples of electronic files that most users of computer systems would wish to store persistently. In a typical personal computer, these and other types of electronic files are stored on a hard disk drive, or increasingly, on a solid state memory device (e.g., a flash drive).
One concern for computer users is the loss of electronic files and data. Hard drives are mechanical devices that, like any other machine, are subject to wear or damage that can lead to a malfunction wherein the information they contain may become partly or completely inaccessible. The likelihood of data loss is sometimes reduced through the use of a redundant array of independent drives (RAID). RAID is a technique wherein multiple hard drives are combined into a larger logical unit, and provides increased reliability though redundancy. Data that is stored to the logical unit is distributed among the multiple drives along with error recovery data. If one physical hard drive fails, only the portions of the data stored to that drive become inaccessible. The inaccessible data is able to be recovered or recreated based on the error recovery data stored on the remaining drives.